Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1996-07-08
1997-11-18
Cain, Edward J.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
524500, C09D13308
Patent
active
056888538
DESCRIPTION:
BRIEF SUMMARY
This application claims benefit of international application PCT/AU94/00600, filed Sep. 29, 1994.
TECHNICAL FIELD OF THE INVENTION
This invention relates to water-borne coatings and in particular to coatings that exhibit good soil resistance properties.
BACKGROUND OF THE INVENTION
The appearance of coatings can be adversely affected by atmospheric pollutants such as dirt, dust and carbon particles from combustion processes being deposited on the surface of a paint film. For example, a white paint film may become quite grey from atmospheric pollutants after exterior use in major industrial cities. In some industrial urban environments unacceptable soiling may take place within as short a period of time as several weeks. The problem of atmospheric soiling is obviously of greatest concern for exterior coatings.
In many cases the soiling of the paint film surface is not able to be rectified by washing by natural rainfall or artificial means. It is believed this relatively permanent soiling is due to the soiling particles becoming embedded in the paint film. This effect can be exacerbated by exposure in tropical climates where heat and high rainfall may contribute to softening of a thermoplastic paint film. It is believed a rough surface contributes to dirt particles becoming entrapped. In practice, however, it appears that gloss and semi-gloss paints which contain high levels of thermoplastic polymer latex binder exhibit the most severe soiling problems, particularly under hot and humid conditions.
Soil resistance needs to be distinguished from stain resistance which is a property more commonly associated with interior paints which are exposed to a range of domestic staining materials such as food, oil and beverages. Indeed paints that are good for stain resistance may be poor for soil resistance and vice versa. For example, water-borne semi-gloss latex paints generally are good for stain resistance and stain removal when used as interior paints. These paints have good mar resistance and wet and dry scrub performance and this enables the stained or dirtied surface to be cleaned by scrubbing without causing the treated area to "gloss up" and exhibit a gloss that is different from the surrounding area. However, when used as exterior paints these same paints can have poor soil resistance.
For exterior paints various methods have been proposed to improve their soil resistance. One method is to use a self cleaning paint film which, while it may become dirty to a similar extent to a standard paint surface, cleans itself by the surface of the paint film being eroded on exposure to the combined effects of atmospheric oxygen, UV radiation and rainfall. This erosion exposes a new surface with clean appearance. These coatings are also known as self chalking paints. Whilst overcoming the problems of soiling to a certain extent they suffer from the problem of still becoming soiled and remaining so until film degradation leads to the apparent cleaning of the surface. As discussed previously, unacceptable soiling can take place in a matter of weeks, yet erosion by degradation is a relatively slow process taking many months before it becomes significant. Another obvious deficiency with such coatings is that because the coating film is gradually being eroded the gloss of the film is reduced with time and also more frequent repainting is required. They are thus less suitable in gloss and semi-gloss formulations.
Another approach to achieving soil resistant exterior coatings has been to modify the surface of a coating film so that the adhesion of soiling particles to the surface is reduced. In an article "A Soil Resistant Treatment For Low Gloss Coatings" by D. L. Gauntt et al, Journal of Coating Technology, Vol 63 No. 803 page 25 December 1991, a treatment suitable for use on military aircraft is described. This article details the use of an unpigmented colloidal silica treatment to be applied to an existing paint film. It is proposed that good soil resistance is achieved in practice because the surface charge of the resu
REFERENCES:
patent: 4069186 (1978-01-01), Ramig
patent: 4385152 (1983-05-01), Boyack et al.
patent: 5308890 (1994-05-01), Snyder
Leary Bruce
Meekings Craig D.
Salter Elizabeth A.
Cain Edward J.
ICI Australia Operations Proprietary Limited
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